The long term goal of this research is to determine the way in which the sex hormones modulate the immune system in mucosal tissues. Studies in the past year have used the genital tract of the rat as a model system. Observations made by the applicant indicate that immunoglobulin A (IgA) and G (IgG) in uterine secretions are under the influence of estrogen. Both immunoglobulins change during the estrous cycle with highest levels measured at proestrus and estrus. These changes appear to be under direct estrogen control because estradiol administered to overiectomized or hypophysectomized rats increases uterine IgA and IgG. In contrast, other steroids such as progesterone, dihydrotestosterone and cortisol have no effect.